Activation of the renin-angiotensin-aldosterone system (RAAS) has been identified as a risk factor for the development of ischemic heart disease, whereas pharmacological interruption of the RAAS with angiotensin-converting enzyme (ACE) inhibitors reduces the development of atherosclerosis in animal models and in patients with coronary artery disease. Although multiple mechanisms may contribute to this association between the RAAS and atherosclerotic events, we have focused on the effects of the RAAS on the plasminogen activator system, which serves as one of the major endogenous defense mechanisms against intravascular thrombosis and plays a critical role in vascular and tissue remodeling. Our group and others have shown that both angiotensin (Ang) II and nitric oxide synthase inhibition stimulate plasminogen activator inhibitor (PAI-1) expression, whereas bradykinin stimulates nitric oxide production and tissue-type plasminogen activator (t-PA) release. Furthermore, we have shown in patients post-MI, in healthy subjects on a low-salt diet, in normotensive post-menopausal women, and in hypertensive, insulin-resistant subjects that ACE inhibition decreases plasma PAI-1 levels and favorably affects fibrinolytic balance. The central hypothesis of the mechanistic studies presented in this proposal is that bradykinin mediates both of the desirable effects of ACE inhibition on vascular fibrinolytic balance by lowering PAI-1 through a nitric oxide-dependent mechanism and by increasing t-PA through a nitric oxide-independent pathway. In Specific Aim 1, we will determine the effect of a specific bradykinin receptor antagonist on the hemodynamic and fibrinolytic responses to chronic ACE inhibition in patients with essential hypertension. In Specific Aim 2, we will use pharmacologic tools that increase (L-arginine) or decrease (L-NAME) the availability of nitric oxide to test the hypothesis that nitric oxide contributes to the favorable effects of ACE inhibition on PAI-1 in humans. In both of these Specific Aims we will examine the interactive effect of a common 4G/5G polymorphism in the PAI-1 promoter on the contributions of bradykinin and nitric oxide to the fibrinolytic response to ACE inhibition. In Specific Aim 3, we will test the hypothesis that bradykinin stimulates t-PA release through a ouabain-sensitive pathway, a non-nitric oxide-dependent pathway. It is anticipated that these studies will generate critical new information regarding the mechanisms through which the RAA and kallikrein-kinin systems regulate vascular fibrinolytic function.